Glutathione peroxidase is an enzyme which catalyzes a reaction of two moles of glutathione and one mole of hydrogen peroxide to form two moles of glutathione-oxide and two moles of water, and is found in mammalian tissues and organs such as liver, kidney, heart, lung, red blood cells and blood plasma. [Flohe, L. et al., FEBS Letters, 32: 132-134 (1973)]It plays an important role in the treatment of biological peroxide by catalyzing the reduction by two electrons of lipid-peroxide with glutathione. Glutathione peroxidase is a protein containing selenium which has the amino acid selenocystein (Sec) in its active center. According to a study on a cloned mouse glutathione peroxidase gene, the opal codon, TGA, of the corresponding ribonucleic acid sequence (RNA), which is in general a termination codon, in this enzyme codes for selenocystein (Sec) [EMBO J., Vol. 5, No 6, pp. 1221-1227 (1986)].
A human-type glutathione peroxide (hereinafter sometimes designated h-GSHPx) has been separated from erythrocyte and blood plasma, and has been known to be a homotetramar, in which the molecular weight of the four erythrocyte type subunits thereof is each 20,600 and that of the blood plasma type subunits is each 21,500. [Archives of Biochemistry and Biophysics, Vol. 256, (2): 677-686 (1987) and The Journal of Biological Chemistry, Vol. 262 (36): pp. 17398-17403 (1987)]
h-GSHPx's derived from erythrocytes, liver and kidney are believed to be identical due to their strong immunological cross reactivity and similar subunit molecular weight of approximately 20,600. The h-GSHPx gene is quite homologous to the mouse GSHPx gene, however the mouse h-GSHPx gene product shares little immunological similarity with h-GSHPx derived from blood plasma. Hence at present more than two kinds of h-GSHPx are known.
These h-GSHPx's were cloned from a c-DNA library of m-RNA isolated from liver and kidney cells, and their gene structure has been determined. [Nucleic Acids Research, Vol. 15, No. 13, pp. 5484 (1987), ibid., Vol. 15, No. 17, pp. 7178 (19870]. Although h-GSHPx protein of blood plasma has been isolated, its gene has not been cloned.